This invention relates generally to a portable pump for dispensing liquid, and more particularly to such a pump having a one-piece piston member adapted for carrying out various valving functions thereby reducing the number of parts and rendering the pump easy and efficient to operate.
Prior dispensing pumps of the class herein described generally include a pump plunger in the form of a stem projecting into a valve element which is arranged for reciprocation in a pump chamber and which is provided with an outlet valve seat facing the chamber. The stem is arranged for axial shifting movement relative to the valve element, and has some type of valve member at a terminal end thereof which shifts away from the outlet valve seat upon an initial depression of the stem to thereby open the outlet to permit liquid to be dispensed through an outlet passage extending through the stem upon a further depression of the stem effecting the piston downstroke movement. Pump constructions of this type, however, typically require multiple parts which are specifically configured for carrying out the dispensing operation including inlet opening and closing, outlet opening and closing and container vent opening and closing functions. Moreover, critical dimensions and tolerances are oftentimes required thereby adding to the cost of construction and operation.